The present invention generally relates to syringe/conduit combinations having a frustoconical male slip fitting and a frustoconical female slip fitting, the male slip fitting being inserted or insertable into the female slip fitting establishing a press fitted connection. The conduit part may for instance be a needle assembly or via which a fluid can be injected into a medical tubing, a bag or a catheter.
Syringes are typically joined to downstream tubing by connecting matching fittings on the distal end of the syringe and a proximal end of the conduit part. One common connector type has matching male and female fittings each having conical surfaces that, when the fittings are connected, provide a sealed press fit connection between tubes. Conical fittings that form a seal by pressing the fittings together are often referred to as “slip fittings” Conical fittings that also include a form locked axial load transfer, such as threaded elements or a bayonet fitting are often referred to as “lock fittings.”
Standards have been developed to permit compatibility of standard fittings. An example of specifications for conical fittings used for medical applications may be found, for example, in the International Standard ISO 594-1 titled “Conical fittings with 6% (Luer) Taper for syringes, needles and certain other medical equipment,” and referred to herein as the “ISO Luer Standard.”
FIGS. 1 through 3 slip fitting conforming to the ISO Luer Standard are shown, where FIG. 1 is a side view of a male slip fitting 10 and a matching female slip fitting 20, and FIG. 2 is a sectional view along the line II-II in FIG. 1.
The male slip fitting 10 has an external frustoconical surface 11 and a distal end 16 for inserting into female slip fitting 20. The female slip fitting 20 has an internal frustoconical surface 21 matching at least a portion of the external frustoconical surface 11 of the male slip fitting 10.
The slip fittings 10 and 20 each have conical surfaces resulting in a conical angle θ, as shown. According to the ISO Luer Standard, the value of this conical angle is 6°. The external frustoconical surface 11 of the male slip fitting 10 has a height A from a proximal base 17 to the distal end 16 having a diameter B. The internal frustoconical surface 21 of the female slip fitting 20 has a depth D extending from an opening with a diameter C to a bottom end 26. The height A, diameters B and C and depth D, are mandated by the ISO Luer Standard, and define contacting surfaces.
FIG. 3 is a sectional view along the line II-II in FIG. 1, but with the male and female slip fittings 10 and 20 connected by applying an axial pressure force of 27.5 N for 5 s whilst twisting action if any is limited to a torque value not exceeding 0.1 Nm to give rotation not exceeding 90°. Such an engagement force is also called an axial engagement force or normalized axial engagement force, and is applied such that a portion of frustoconical surfaces 11 and 21 are in contact, where the contact portion is indicated by the length X. The ISO Luer Standard mandates that the distal end 16 and bottom end 26 be separated by a distance, which is indicated as E=X−D. The value of E is not specified by the ISO Luer Standard, but is required to be greater than zero. In practice, in ISO Luer Standard compliant fittings, the distance E is typically about 2 mm or more and the diameter B is approximately 4 mm, so that, a “dead space” 300 within connected fittings 10 and 20 of approximately 40 μl is left, in addition to the dead space constituted by the channels in the syringe part and in the conduit part. Medicament volumes left in this dead space constitute a waste of medicament and associated costs, in particular when expensive drugs are administered. Medicament leftovers in the dead space may also constitute an environmental and/or health hazard.
Other, functional requirements of the ISO Luer Standard are that after a slip type connection has been made, to prevent inadvertent disconnection, the slip type connection should resist an axial removal force of 35 Newton and unscrewing torque of up to 0.02 Nm without disconnection. In addition, slip type connections should also hold a seal against 3 bar after a connection has been made. In slip fitting connections this resistance and sealing is supplied by the friction between the opposing conical surfaces.